Stepper Motor Generator Diagram

Stepper motors are a
subject that keeps recurring. This little circuit changes a clock signal
(from a square wave generator) into signals with a 90-degree phase
difference, which are required to drive the stepper motor windings. The
price we pay for the simplicity is that the frequency is reduced by a
factor of four. This isn’t really a problem, since we just have to
increase the input frequency to compensate. The timing diagram clearly
shows that the counter outputs of the 4017 are combined using inverting
OR gates to produce two square waves with a phase difference. This
creates the correct sequence for powering the windings: the first
winding is negative and the second positive, both windings are negative,
the first winding is positive and the second negative, and finally both
windings are positive.

Stepper Motor Generator Circuit

Stepper Motor Generator Circuit Diagram

Internally, the 4017 has a divide-by-10 counter followed by a
decoder. Output ‘0’ is active (logic one) as long as the internal
counter is at zero. At the next positive edge of the clock signal the
counter increments to 1 and output ‘1’ becomes active. This continues
until output ‘4’ becomes a logic one. This signal is connected to the
reset input, which immediately resets the counter to the ‘zero’ state.
If you were to use an oscilloscope to look at this output, you would
have to set it up very precisely before you would be able to see this
pulse; that’s how short it is. The output of an OR gate can only supply
several mA, which is obviously much too little to drive a stepper motor
directly. A suitable driver circuit, which goes between the generator
and stepper motor.

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